By Paul Rincon
Science reporter, BBC News
The impact occurred about 1.2 billion years ago.
Evidence of the biggest meteorite ever to hit the British Isles has been found by a team of scientists.
Researchers from the universities of Oxford and Aberdeen think a large object hit north-west Scotland about 1.2 billion years ago.
The space rock struck the ground near the present-day town of Ullapool, they report in Geology journal.
The scientists found what they believe to be debris which was flung out when the impact crater was formed.
"If there had been human observers in Scotland 1.2 billion years ago, they would have seen quite a show," said co-author Ken Amor, from the University of Oxford.
"The massive impact would have melted rocks and thrown up an enormous cloud of vapour that scattered material over a large part of the region around Ullapool. The crater was rapidly buried by sandstone which helped to preserve the evidence."
The crater is suspected to lie under the Minch, the waterway that separates Lewis in the Outer Hebrides from the north-west Highlands of Scotland.
Unusual rock formations in the area were previously thought to have been formed by volcanic activity.
But Ken Amor and his colleagues found "ejecta blanket" evidence buried in rocks from the area. This represents debris thrown out when the huge object slammed into the ground.
Ejected material from the meteorite strike is scattered over an area about 50km across.
In the rocks, the researchers found elevated levels of the element iridium, which is characteristic of extra-terrestrial material. They also found microscopic parallel fractures that also imply a meteorite strike.
Co-author John Parnell, a geologist at the University of Aberdeen, said: "Building up the evidence has been painstaking, but has resulted in proof of the largest meteorite strike known in the British Isles."
Mr Amor said this was the "most spectacular evidence for a meteorite impact within the British Isles found to date".
He added: "What we have discovered about this meteorite strike could help us to understand the ancient impacts that shaped the surface of other planets, such as Mars."
The proposed volcanic origin for the rock formations had previously been a puzzle, as there are no volcanic vents or other volcanic sediments nearby.
The UK's only other known space impact location is Silverpit in the North Sea. Scientists have found evidence on the sea floor for a cataclysmic asteroid or comet strike that occurred some 60-65 million years ago. The impact structure is about 130km (80 miles) east of the Yorkshire coast.
Some researchers, though, have questioned its space origins.